1. Field of the Invention
This invention lies in the field of rotary drilling of oil and gas wells. More particularly, it concerns method and apparatus for determining if, and when, gas enters the drilling well at a point near the bottom of the well, from a formation into which the well is being drilled, or through which it has been drilled.
Still more particularly, it concerns apparatus and method for detecting the presence of gas entering the well at the time the gas-containing formation is penetrated, and without the necessity of waiting until the first sample of gas flowing into the mud column reaches the surface.
2. Description of the Prior Art
In the prior art there has been no way of detecting just when a gas-containing geologic formation is penetrated by the bit, and/or gas under a pressure greater than the mud pressure in the well can flow into the mud column, and up the annulus of the well to the surface. The only method of detection was to wait for a period of time sufficient for the flow of mud from the bottom of the well to the surface, and to detect the presence of gas in the outflow of mud from the casing. By the method of this invention it should be possible to detect almost immediately the injection of gas from the formation into the well.